Multi-stage screening arrangements are constructed usually in such a manner that several screening units are arranged behind each other and usually each unit includes a device for the retaining of the coarse material, that is, a screen or similar arrangement, and a device for the removal of the coarse material, that is, an up and down movable or continuously movable screen cleaner, as well as device for transporting away the coarse material resulting from the screening. In order words, the required equipment outlay of a multi-stage screening arrangement is usually proportional to the number of the stages present. Such large structural outlay affects equally the space, machine-technical, control technical, the operating and service technical and costs considerations as well.
In the screening arrangement according to German Laid-Open Application No. 2,304,600 and German Pat. No. 905,118 the large structure is simplified in that the screening devices are set up with a distance with respect to each other and are cleaned one after the other by a single cleaning arrangement. This known arrangement still requires a great deal of mechnical outlay. In addition, the time element required for the cleaning is twice as large as required for the cleaning of a single screen.
German Pat. No. 44,143 discloses uncleaned screens which are set up behind each other with a distance following each other as a second stage for the additional retention of coarse material.